Mechanical behavior of fuel cell membranes under humidity cycles and effect of swelling anisotropy on the fatigue stresses

The mechanical response of proton exchange membranes in a fuel cell assembly is investigated under humidity cycles at a constant temperature (85 °C). The behavior of the membrane under hydration–dehydration cycles is simulated by imposing a humidity gradient from the cathode to the anode. Linear elastic, plastic constitutive behavior with isotropic hardening and temperature and humidity dependent material properties are utilized in the simulations for the membrane. The evolution of the stresses and plastic deformation during the humidity cycles are determined using finite element analysis for two clamping methods and various levels of swelling anisotropy. The membrane response strongly depends on the swelling anisotropy where the stress amplitude decreases with increasing anisotropy. These results suggest that it may be possible to optimize a membrane with respect to swelling anisotropy to achieve better fatigue resistance, potentially enhancing the durability of fuel cell membranes.     

描述膨胀页岩的新模型

页岩膨胀是一个很复杂的问题,很多细致入微的描述由于在实践中无法对其参数有效确定,都无法给工程人员提供确定的认识和指导,为此介绍了一种简化而且实用的膨胀页岩模型.该模型通过进一步明确膨胀页岩层问的晶隙水和孔隙水2者之间的相互关系,建立了2者之间的力学和化学平衡方程.该模型清楚地表示,页岩的膨胀黏土晶隙水的活度是对其应力环境敏感的,应力的改变将直接导致其活度变化,实验室常压下直接测定页岩岩心的水活度不能代表其在地下应力状态下的情况.     

致癌染料——芳香胺的致癌机理

论述了癌肿病因进程的三个阶段，化学致癌物质，尤其是致癌染料的致癌机理，以及国际宣布的２２个致癌芳香胺中间体。     

Behaviors of Acrylamide/Itaconic Acid Hydrogels in Uptake of Uranyl Ions from Aqueous Solutions

Abstract

In this study, adsorptions of uranyl ions from two different aqueous uranyl solutions by acrylamide-itaconic acid hydrogels were investigated by a spectroscopic method. The hydrogels were prepared by irradiating with γ-radiation. In the experiment of uranyl ions adsorption, Type II adsorption was found. One gram of acrylamide-itaconic acid hydrogels sorbed 178–219 mg uranyl ions from the solutions of uranyl acetate, 42–76 mg uranyl ions from the aqueous solutions of uranyl nitrate, while acrylamide hydrogel did not sorb any uranyl ion. For the hydrogel containing 40 mg of itaconic acid and irradiated to 3.73 kGy, swelling of the hydrogels was observed in water (1660%), in the aqueous solution of uranyl acetate (730%), and in the aqueous solution of uranyl nitrate (580%). Diffusions of water onto hydrogels were a non-Fickian type of diffusion, whereas diffusions of uranyl ions were a Fickian type of diffusion.     

Gas transport parameters of differently compacted granulated bentonite mixtures (GBMs) under air-dried conditions

Granulated bentonite mixtures (GBMs) have been regarded as effective buffer materials in the deep geological disposal of radioactive waste due to their operational advantages, such as ease of transportation and in-situ placement/backfilling. Many studies have been done to characterize the hydraulic and thermal properties of GBMs as well as their swelling properties. Only limited studies, however, have investigated their gas transport properties, even though these properties affect their compactness during in-situ placement/backfilling and subsequent gas diffusion and advection in the buffer zone. The aim of this study is to understand the gas transport parameters, i.e., air permeability (k_a) and gas diffusivity (D_p/D_o), of tested samples compacted at different dry densities (DDs) under air-dried conditions, linking them with the measured density distribution characteristics determined by microfocus X-ray computed tomography (MFXCT) analysis. Two types of GBMs were used in this study: 1) FE-GBM (prepared from National Standard® bentonite, Wyoming, USA): this material was used in the Full-scale Emplacement (FE) experiment at the Mont Terri rock laboratory, Switzerland) and 2) OK-GBM (prepared from a bentonite, originating from Japan, with the trade name of OK bentonite, Kunimine Industries). The tested samples were firstly packed in a 100-cm³ acrylic core with different DDs, ranging from loose to dense (1.09 to 1.75 g/cm³), and scanned by MFXCT. The weighting factors, w_f (fine fraction; lower density) and w_c (coarse fraction; higher density) (w_f + w_c = 1), were determined after the peak separation of the measured CT brightness histograms from the reconstructed three-dimensional multiplanar reconstruction (MPR) images of the MFXCT analysis. The measured k_a and D_p/D_o were highly dependent on the DDs, the k_a (?) values fitted well with a power law model, and the D_p/D_o (?) was predicted accurately by several previously proposed models. For both FE-GBM and OK-GBM, there were good linear relationships between the gas transport parameters and w_c × DD, implying that the weight of the coarse fraction controlled k_a and D_p/D_o. Moreover, the Kozeny-Carman model, incorporating the measured volumetric surfaces from the MFXCT analysis, was able to predict the k_a values well.     

Lyocell织物碱处理的应用研究

Lyocell织物的染整加工依然是染整界的一项技术难题。本文研究对Lyocell织物采用烧碱处理以改变织物的性能，并得到了较为满意的结果。     

W/O/W emulsions with high internal droplet volume fraction

We prepared water-in-oil-in-water (W/O/W) double emulsions with high internal aqueous droplet fraction using food-based ingredients. These compartmentalised materials were comprised of oil globules dispersed in an external aqueous phase, with the globules themselves containing densely packed inner aqueous droplets. We were able to obtain double emulsions with large globule fractions (up to 45 vol.%) using only 5 vol.% oil (relative to the overall composition). In the final state, the inner droplet fraction within the globules could exceed 90 vol.%. The method was based on two successive emulsification steps, followed by osmotic swelling (transport of water from the external phase to the inner droplets through the oil phase). During the final step, the swelling was controlled by the osmotic pressure mismatch between the external and internal aqueous phases using solutes dissolved at different concentrations. The osmotic swelling model of Mezzenga et al. (Langmuir, 2004, 20, 3574-3582) was re-adapted in the limit of small Laplace pressures to predict the final composition resulting from osmotic equilibration. The internal droplet fraction was lower than that predicted by the model as a consequence of coalescence phenomena occurring during the swelling process. The proposed approach constitutes a valuable guide within the prospect of formulating emulsions with enhanced encapsulation capacity and reduced fat content.     

Milling of rice grains: The roles of starch structures in the solubility and swelling properties of rice flour

Rice flours with different particle sizes and degrees of damaged starch granules were produced by hammer milling and cryogenic milling of rice grains, where degradation of starch molecules was evident in the hammer‐milled flours, but not in the cryogenically milled flours. The solubility and swelling properties of the resulting rice flours were determined in cold (30°C) and hot water (90°C). The cold‐ and hot‐water starch solubility was strongly correlated with the degree of damaged starch granules, and weakly with the particle size of rice flour. No evident correlations were observed between starch solubility and the molecular structures, indicating that molecular degradation by milling process was not the only precondition of increased starch solubility. Possible mechanism for the observed correlations is that increasing surface area and/or exposure of loosely packed inner part of starch granules with increasing degree of damaged starch granules allowed more starch molecules to leach out in cold and hot water. Furthermore, the cold‐water swelling of rice flour was strongly correlated with the degree of damaged starch granules, possibly due to the rapid hydration of damaged starch granules, whereas the hot‐water swelling did not show any correlations with flour particle size and granular and molecular starch structures. The results have provided better insights in the relationship between starch structures and solubility and swelling properties of rice flour, which can be used to improve the manufacture and selection criteria of rice flour for better products.     

Evaluation of rate of swelling and erosion of verapamil (VRP) sustained-release matrix tablets

Tablets manufactured in-house were compared to a marketed sustained-release product of verapamil to investigate the rate of hydration, erosion, and drug-release mechanism by measuring the wet and subsequent dry weights of the products. Swelling and erosion rates depended on the polymer and granulating fluid used, which ultimately pointed to their permeability characteristics. Erosion rate of the marketed product was highest, which suggests that the gel layer that formed around these tablets was weak as opposed to the robust and resistant layers of test products. Anomalous and near zero-order transport mechanisms were dominant in tests and commercial product, respectively.